Monolithic Memories

Bulletin Board

EPA is currently evaluating the potential for vapor intrusion in buildings overlying the shallow groundwater contamination area. On December 3, 2013 EPA sent a letter to the State of California's Regional Water Quality Control Board providing guidelines for vapor intrusion sampling and evaluation at this and 10 other South Bay State-lead sites.

Description and History

NPL Listing History

NPL Status: Final

Proposed Date: 10/15/84

Final Date: 07/22/87

Deleted Date:

Monolithic Memories manufactured integrated circuits on this 20-acre site. The facility consists of four buildings that were used for production, assembly, storage, offices, and laboratories. In 1982, monitoring wells on the site were found to be contaminated with volatile organic compounds (VOCs). Contamination probably resulted from leaking pipes in solvent waste drains. The company has removed two subsurface waste solvent tanks and two subsurface acid neutralization systems. In 1986, under the direction of the State, the company began pumping and treating the groundwater to contain the contaminant plume. The property was purchased by Advanced Micro Devices (AMD) in 1987, and the company has assumed the ongoing activities. The contaminant plume has merged with the National Semiconductor plume (located immediately upgradient of Monolithic). This is one of 28 sites in the South Bay Area of San Francisco. Facilities at these sites have used a variety of toxic chemicals, primarily chlorinated organic solvents, which have contaminated a common groundwater basin. Although the sites are listed separately on the NPL, the EPA intends to combine cleanup activities at some of the sites as part of an area-wide approach to cleaning up the contamination. Approximately 300,000 people live within 3 miles of the site and depend on groundwater as their source of drinking water. A medical clinic is adjacent to the site.

Contaminants and Risks

Contaminated Media

Groundwater

Soil and Sludges

The groundwater and soil are contaminated with various VOCs. While there is no current pathway through which people can come into contact with contaminants, people who ingest or come into direct contact with contaminated groundwater or soil may be at risk.

Who is Involved

Investigation and Cleanup Activities

Initial Actions

Immediate Actions: Under State oversight, Monolithic Memories has been extracting and treating groundwater since 1986.

Cleanup Ongoing

Entire site: Monolithic Memories completed an investigation determining the type and extent of contamination at the site. Based on the results of the investigation, the EPA selected remedies for the final cleanup of the site which include continuing to extract and treat the contaminated groundwater and treating contaminated soil through vapor extraction. Cleanup activities are underway.

The site is being cleaned up under orders from the California Regional Water Quality Control Board.

Cleanup Results to Date

Construction for all cleanup remedies is complete. The groundwater extraction and treatment system continues to reduce the potential for exposure to contaminated groundwater at the Monolithic Memories site while cleanup of soil contamination continues.

The Third Five Year Review was completed in September 2009 and concluded that:
Although the historical groundwater plume was reduced and contained, current information indicates that the selected remedy may not be able to restore the groundwater to its beneficial use as a potential drinking water supply. The recent PCE spill has increased concentrations on property and has not been fully assessed. Currently, the institutional controls are preventing exposure to, and the ingestion of, contaminated groundwater. The feasibility of alternative remedies or improvements to the existing system need to be evaluated to insure the long term remedial objectives are achieved.